Process and device for regulating drafting equipment, in particular in carding machines

ABSTRACT

A method of regulating a drafting arrangement, in which measuring signals are acquired at a feed end of the drafting arrangement, compared with a set value to provide a differential signal, and an adjusting signal for the control unit of a variable speed motor for the pair of drafting rollers is derived from the differential signal, provides reliable control results and adjustment of the sliver where a difference has been detected. Set values are entered by a transfer address from a set-point register. The basic speed is derived from actual speed of a doffer and supplied as basic voltage to the control unit of the variable speed motor. A measuring clock pulse of low frequency is generated, dependent upon a roller of the drafting arrangement. With every measuring clock pulse a measuring signal is obtained, converted into a digital signal, compared with the activated transfer address of the set-point register and a differential signal is generated. The differential signal obtained is transformed into a transfer address for a correction register, and that the control value read by the activated address in the correction register is supplied to the control unit of the variable speed motor. The invention also relates to a regulating device for carrying out the disclosed method.

BACKGROUND OF THE INVENTION

The invention relates to a method of regulating a drafting arrangementand, more particularly, to a method of regulating a drafting arrangementin which inconsistencies in thickness of a sliver are corrected duringthe drafting process. The invention also relates to a regulating devicefor carrying out the method.

Methods directed to achieving such regulation of a drafting arrangementhave been addressed in the art, one such method described for example inGerman DE-OS 36 22 584. In accordance with the disclosed method, thethickness of the sliver is measured at the feed and delivery ends of thedrafting arrangement. The measured values are evaluated with a timedelay and, depending on the measured mass per unit of length and a setvalue for the mass per unit of length, are converted into an adjustingsignal. From the difference between the measured mass and the presetvalue, a desired value is obtained by means of a first regulatingcircuit. This target value and a mass deviation evaluated with a timedelay are used to generate, by means of a second regulating circuit, acorrecting variable for setting the draft of the drafting arrangement.

This type of procedure has considerable disadvantages. For example, thedraft may not always be reliably corrected exactly where the deviationfrom the set value has been detected within the sliver. Although theevaluation of the second measuring signal and the second control actionreduces the probability of possible error thereby increasing likelihoodof achieving an accurate, deviation-controlled drafted sliver ascompared with a system with a single means for regulation, there stillremains a chance of error.

In another regulating process described in German DE 42 02 352 A1,measuring devices are also arranged at the feed and delivery ends of thedrafting arrangement and their measured values are compared with oneanother. The result is corrected by means of stored information andconverted into an adjusting signal.

Such a regulator is relatively expensive, and the thickness of thesliver ascertained at the feed end of the drafting arrangement is notalways corrected where necessary.

In this method it has been suggested that the time delay from themeasuring point at the feed end of the drafting arrangement to the timeof the output of the correcting command be represented as a variable ofcertain empirical values and other parameters. However, the resultsobtained in this way are still unsatisfactory insofar as random factorscannot be excluded (DE 42 15 682 and 42 02 352).

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod of regulating a drafting arrangement which overcomes thedrawbacks of the prior art.

It is a further object of the present invention to provide a method ofregulating a drafting arrangement in which the thickness of the sliveris reliably corrected in the place where the deviation has beendetected.

It is still a further object of the invention to provide a device forcarrying out the regulation method in a form which provides ease ofoperation and low maintenance, and which guarantees consistently goodcontrol results at any adjusted speed of the machine.

Briefly stated, the invention relates to a method of regulating adrafting arrangement, in which measuring signals are acquired at a feedend of the drafting arrangement, compared with a set value to provide adifferential signal, and an adjusting signal for the control unit of avariable speed motor for the pair of drafting rollers is derived fromthe differential signal, provides reliable control results andadjustment of the sliver where a difference has been detected. Setvalues are entered by a transfer address from a set-point register. Thebasic speed is derived from actual speed of a doffer and supplied asbasic voltage to the control unit of the variable speed motor. Ameasuring clock pulse of low frequency is generated, dependent upon aroller of the drafting arrangement. With every measuring clock pulse ameasuring signal is obtained, converted into a digital signal, comparedwith the activated transfer address of the set-point register and adifferential signal is generated. The differential signal obtained istransformed into a transfer address for a correction register, and thatthe control value read by the activated address in the correctionregister is supplied to the control unit of the variable speed motor.

According to the present invention, the above objectives areaccomplished by a method in which a low-frequency measuring clock pulseis generated in response to and dependent upon rotation of a roller ofthe drafting arrangement. A measuring signal is acquired at the feed endof the drafting arrangement in response to the clock pulse and convertedinto a digital signal. The set values are entered by a transfer addressfrom a set-point register. The digital signals are compared with a setvalue in the activated transfer address of the set-point register and adifferential signal is generated. The determined differential signal istransformed into a transfer address for a correction register. Then, acontrol value is read by the activated address in the correctionregister and an adjusting signal is derived for the control unit of thevariable speed motor for the pair of drafting rollers based upon thedifferential signal. The adjusting signal is then supplied to thecontrol unit of the variable speed motor.

Since the set value is permanently available in the form of a set-pointaddress from a set-point register and a signal for the basic speed ofthe motor to be regulated, the processing of a measuring signal limitedmerely to its conversion into a digital signal and the transformationinto a transfer address while processing the set value.

The command adjusted by the transfer address for correcting the drivingvoltage of the variable speed motor remains unchanged in its conditionuntil the next correction value is obtained, and it can feed the setcorrection value into the variable speed motor over extended periods oftime. The variable speed motor has sufficient time to correct itsmagnetic fields and to accelerate and decelerate the mechanicalelements, rotor and drawing-in rollers to the new speed value. At theend of the acceleration, at usual sliver speeds and in usual dimensionsof the drafting arrangement, the sliver sections, which havepredetermined the value of the measuring signal, are within the sphereof action of the pair of drafting rollers. It has turned out that verygood control results can also be obtained at higher sliver speeds, forexample, as high as 250 m/min.

The present invention further provides an embodiment of the method whichguarantees that, with simple and low-cost components, the set values canbe made available for long periods of time and easily adapted to newconditions. The embodiment includes conversion of the analogue presetvalue into a digital signal by an A-D converter, and transformation ofthe digital signal into a transfer address for the set-point register.

According to a feature of the invention, there is further provided amethod in which the measuring clock pulse is obtained by a sensor whichthereby allows a compact design of the controller without interferingwith other devices of the machine.

The present invention further includes a feature in which the controlvalue provided for the basic speeds of the variable speed motor isobtained as a digital speed pulse, and converted into a voltage signalby an electronic processing unit. The voltage signal then supplied tothe control unit for the variable speed motor, and has the advantagethat the synchronism between doffer and drafting arrangement isguaranteed under all conditions.

In accordance with a further feature of the invention, in the event of apower failure, the synchronism can be maintained by the use ofappropriate energy stores for the information transmission and for thecontrol of the variable speed motor.

Yet a further embodiment of the invention directed to a device forpracticing the above method, guarantees a high quality of the controlresults with simple, currently available components.

In accordance with a feature of the invention directed to the abovedevice a pair of measuring rollers is provided, of which at least oneroller revolves in connection with the pair of drawing-in rollers.Further, the driving connection between neighboring pairs of rollerscustomary for can coilers can be used as a structural component.

In a further embodiment, one of the drawing-in rollers has at least fourgenerator marks, staggered to one another by almost the same angularintervals, to which a fixed sensor is allocated. The measuring rollersare arranged to the drawing-in rollers, and the drawing-in rollers arearranged to the drafting rollers along the travelling direction of thesilver and staggered by about 50 mm each. These angles and spacingsresult in the fact that, at the usual sliver speeds, the sliver draft iscorrected where the difference has been detected.

A further feature of the invention provides a device in which a cancoiler for sliver coiling following the drafting arrangement is drivenby a motor, which is indirectly powered in a manner dependent upon thespeed of the variable speed motor of the drafting arrangement, such thatno separate regulating device need be provided for the motor to drivethe can coiler. A sliver storage between drafting arrangement and cancoiler can thus be avoided.

The above, and other objects, features and advantages of the presentinvention will become apparent from the following description read inconjunction with the accompanying drawings, in which like referencenumerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the working elements of theregulated drafting arrangement in connection with a so-called cancoiler;

FIG. 2 is a block diagram of the regulating device for the draftingarrangement; and

FIG. 3 is a schematic representation of the regulating action along atime axis.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a drafting arrangement is located at the deliveryend of a flat card and arranged, in the generally known manner, behindsliver funnel 2. Directly behind funnel 2 and instead of the usual pairof calender rollers, a pair of measuring rollers 30,31 is arranged,which is a component part of a data transmitter 3. The bottom measuringroller 30 is stationary and subject to rotary drive. The top measuringroller 31 runs on bearings, and is vertically movable and loaded. Ameasuring transducer 33 scans the vertical position of the top roller 31and transforms a displacement signal generated thereby into an analogueelectric quantity. In this way, it supplies a signal which isproportional to the thickness of a sliver 1 passing between rollers30,31.

The pair of measuring rollers 30,31 is followed by the pair ofdrawing-in rollers 40,41 at a distance of about 50 mm. The bottom roller40 is also stationary and driven in a certain transmission ratio to adoffer 631 (shown in FIG. 2). The top roller 41 is nonpositively held atthe bottom roller 40. It rotates with the latter and squeezes sliver 1passing through. One of the pair of measuring rollers 40,41 has a numberof generator marks 411 at almost uniform angular distances, which arescanned by a fixed sensor 412. The pulses obtained in this way areconverted into electric clock signals, the measuring clock pulses a, b,. . . .

At another distance of about 50 mm, or any other distance depending onthe mean staple length of sliver 1, a pair of drafting rollers 50,51 isarranged. Each of the rollers of the pair of drafting rollers 50,51 areidentical with those of the pair of drawing-in rollers 40,41. The bottomroller 51 is driven by a variable speed motor 52, which is a servomotor.A processing unit 6 for the draft quantities and a control unit 53 areallocated to variable speed motor 52.

Having passed the pair of drafting rollers 50,51, sliver 1 reaches thearea of the so-called can coiler 7, either directly or indirectly via anintermediate storage 71, and is then conveyed through a pair of coilingrollers 72 according to a given scheme, and coiled in a sliver can 73.The pair of coiling rollers 72 of can coiler 7 is driven by a separatemotor 74 in a known manner. The speed of motor 74 is regulated orcontrolled, respectively, in dependence on the delivery speed of thedrafting arrangement.

Turning now to FIG. 2, the mode of operation of the regulated draftingarrangement shall be described with reference thereto. As mentionedabove, FIG. 2 shows a block diagram of a regulating circuit for variablespeed motor 52 of the pair of drafting rollers 50,51. Data transmitter 3supplies an analogue value of the thickness of sliver 1 directly behindfunnel 2. The analogue signal is fed into an A-D converter 34, whichdigitizes the analogue signals in an 8-bit form. A-D converter 34 isfollowed by a numerical control system 61, whose tasks and componentparts will be described below.

Parallel to this transmission of data, an analogue set value is firstentered at a set-point input 621. This set value operating as areference input is digitized by means of an A-D converter 622 andtransformed into a transfer address by another numerical control system623. The transfer address is used for selecting one of the stored setvalues from a set-point register 6231 and for transferring it tonumerical control system 61 for data transmitter 3.

The set value prepared in this manner is compared with the digitizedmeasured value. Transfer addresses are next defined from thedifferential signal obtained, depending on the value of the difference.Using the transfer addresses from the differential value, a command lineis selected from a correction register 613 whose activated informationis then supplied to control unit 53 for variable speed motor 52.

In addition, control unit 53 is supplied with a control voltage, whichis proportional to the speed of the card's doffer 631. The speed signalis generated by means of an incremental transducer (IGR) 632, whosepulse train is evaluated by a transducer card 633 and transformed intoan equivalent voltage. In control unit 53, the voltage value for thecorrection and the voltage value for the basic speed are added, and anappropriate control command is transmitted to variable speed motor 52.

Variable speed motor 52 is a highly dynamic servomotor, the rotorthereof having an extremely low moment of inertia. According to theselection series, it has a moment of inertia of less than 0.001 kpm².Motor 52 should have a moment of inertia that is big enough forperforming the necessary corrections of the speeds for the pair ofdrafting rollers 50,51 in an adequately short period of time.

Referring now to FIG. 3, another schematic representation of theregulating action along a time axis t is depicted. The time valuesillustrated are not shown accurately proportional to actual values. Thedepicted representation has been chosen in order to demonstrate how theindividual operations are carried out, in sequence within very shortperiods of time, in a manner which guarantees, as exactly as possible,accurate drafting at the point of sliver 1 where the difference has beendetected.

For the first procedure step, i.e. the conversion of the measured valueof the sliver thickness, the A-D converter requires a mean value ofabout 0.8 ms, indicated by an A-D conversion time period W which isinitiated by an initial clock pulse a'. Another 5 to 6 ms are requiredfor the comparison of the measured value and the set value in thecomparator 611 indicated as a comparison time period V, the definitionof the transfer address at 612 for correction register 613 indicated asa definition time period S, as well as the selection of the transferaddress from correction register 613 indicated as a time period A. Thecontrol unit 53 also needs about the same time for outputting thecorrecting variable for the variable speed motor 52.

Variable speed motor 52 again requires some time for the necessary speedcorrection, which is considerably longer than the time needed forprocessing the electric quantities. Only when a perceptible speedvariation occurs, is correction of the sliver thickness by increasing orreducing the draft accomplished.

It must also be taken into consideration that the fibres, which must bedisplaced within sliver 1, are not always, as required, in such africtional connection with the rollers that guarantees their correctdraft. The desired value from the set-point register 6231 is availablefor an unlimited period of time.

The digital output of the measured value by A-D converter 34 allows thecomparison and the definition of the transfer address at the same time.If the transfer address is switched through in correction register 613,A-D converter 34 also receives a signal, which allows the switchingthrough of the next measured value in the next measuring clock pulse b'.

Upon arrival of the next measuring pulse b', the next measured value isentered into the control system and processed in the same manner asdescribed above with regard to the first pulse a'. As soon as the newcurrent address is activated in correction register 613, control unit 53corrects its output and causes variable speed motor 52 to run at the newcorrected speed.

At an assumed mean sliver speed of about 170 m/min, the measured pointof sliver 1 is moved up to the pair of drawing-in rollers 40,41 in about17 ms. The sliver needs another 17 ms to reach the pair of draftingrollers 50,51. With a drafting roller diameter of about 30 mm and fourgenerator marks 411 on one of the pair of drawing-in rollers 40,41, atime interval of about eight to ten milliseconds will be required fromone pulse to the next.

Since no calculating operations are required for determining the setvalue, each new correction value can be provided for variable speedmotor 52 within a very short time. Variable speed motor 52 can start tovary its speed directly after the measuring operation and, as soon asthe next correction value arrives, either finish or continue thecorrection. Apart from the natural tolerances, the correction can becarried out at the time when the measuring point on the sliver 1 ismoving within the range of action of drafting rollers 50,51.

It must also be taken into account that, due to the mean fibre length,the draft range of drafting rollers 50,51 extends almost up to the nipbetween drawing-in rollers 40,41. The measured point on sliver 1 hasreached that area when the motor speed has already changed by asufficient value.

An adequate period of time elapses before the next correction signalarrives, allowing sufficient time for the motor to complete thecorrection according to the values set by the correction register. Thetime period ends when variable speed motor 52 has already undergone aperceptible speed variation based on the new correction signal.

If it turns out that the correction values are too big or too small, avariation can be achieved by modifying the allocation to the commandlines of the correction register, i.e. the address designations.

Triggering of new measuring pulses when the previous control operationis not yet completed should be avoided, particularly a high operatingspeeds. For this purpose, a pulse F is transmitted with the correctionaddress to A-D converter 34 of data transmitter 3, which releases thetransmission of a new measured value to the numerical control system 61.This means that no new measured value can be transmitted until theprevious processing operation for the adjusting signal is completed.

Tests have shown that the control performance for the sliver thicknessis very good at the usual sliver speeds of 170 m/min. Surprisingly,almost ideal control results are achieved at higher speeds (up to 250m/min). The control results obtained at very low speeds, for example, atthe creep speed, are also good because the end of every controloperation is limited by achieving the new speed. The recovery time of anoperation has no effect on the correction value.

The unique aspects of the invention are achieved by virtue of the factthat the time for the provision of a correction value effective inpractice can be kept very short, and motor 52 has sufficient time forreaching the corrected speed before the measured section of sliver 1enters the range of action of drafting rollers 50,51.

In the present example, the supply of transfer addresses and theselection of registers are achieved by means of prepared adjustinginstructions. It is also possible to use very fast computers to supplythe data to be evaluated, and to maintain the supply over a givenangular range of the drafting rollers.

It is further noted, that owing to the differing outgoing speeds ofsliver 1 at the end of the drafting arrangement, it is also necessary todrive the pair of coiling rollers 72 of can coiler 7 at a matched speed.For this purpose, according to convention, an additional regulation canbe allocated to motor 74 arranged there. It is easier, however, tocorrect the speed of motor 74 together with variable speed motor 52. Alow-cost configuration is provided if both motors 74 and 52 areallocated to a single control unit, or if an incremental transducer,whose speed signals directly determine the speed of motor 74, isallocated to variable speed motor 52.

What we claim is:
 1. A method of regulating a drafting arrangement,comprising the steps of:providing a pair of drafting rollers driven by avariable speed motor, a basic speed of which is derived from an actualspeed of a doffer in a preceding operation and determined by a basicvoltage supplied to a control unit of the variable speed motor;generating a low-frequency measuring clock pulse in response to anddependent upon rotation of a roller of the drafting arrangement;entering set values by a transfer address of a set-point register;acquiring a measuring signal at a feed end of the drafting arrangementin response to said clock pulse; converting said measuring signal into adigital signal; comparing said digital signal with a one of said setvalues of the transfer address of said set-point register to obtain adifferential signal; transforming said differential signal into atransfer address for a correction register; reading a control value ofthe transfer address of the correction register; deriving an adjustingsignal for the control unit of the variable speed motor for the pair ofdrafting rollers based upon said control value; and supplying saidadjusting signal to the control unit of the variable speed motor.
 2. Amethod according to claim 1, wherein:each of said set values areconverted into a digital signal by an A-D converter; and said digitalsignal is transformed into said transfer address for said set-pointregister.
 3. A method according to claim 1 or 2 wherein:the draftingarrangement includes a drawing-in roller including at least onegenerating mark formed thereon, said measuring clock pulse beingobtained by a sensor which detects said at least one generating mark. 4.A method according to claim 1 or 2 further including the stepsof:obtaining a digital speed pulse from the doffer; converting saiddigital speed pulse into a voltage signal by an electronic processingunit; and supplying said voltage signal to said control unit for saidvariable speed motor.
 5. A regulating device for a drafting arrangement,comprising:a pair of drawing-in rollers; a pair of drafting rollersrotatably driven by a variable speed motor; a microprocessor-basedcontrol unit including means for adjusting a speed of said variablespeed motor; said variable speed motor being a controllable servomotorincluding a controller with a cycle time, said cycle time being smallerthan 15 ms, and including a rotor having a moment of inertia that issmaller than 0.001 kpm² ; a measuring device in front of said pair ofdrawing-in rollers including means for measuring a thickness of a sliverat a location therealong, said measuring device further including a datatransmitter; said drawing-in rollers being driven at a speed dependentupon that of a doffer of a preceding operation; said drawing-in rollersincluding at least one generator mark formed thereon for producing aclock pulse in response to rotation of said drawing-in rollers; aframe-fixed sensor including means for sensing said at least onegenerator mark and for generating a measuring clock pulse in response toa sensing thereof, said sensor being electrically connected with saiddata transmitter of said measuring device; said measuring device beingfollowed by an A-D converter and a processing unit including a transferaddress definition and a correction register.
 6. A regulating deviceaccording to claim 5, wherein said measuring device includes a pair ofmeasuring rollers, at least one of which revolves in connection withsaid pair of drawing-in rollers.
 7. A regulating device according toclaim 5 or 6, wherein a basic draft of the drafting arrangementcorresponds to a ratio of about 1:1.3.
 8. A regulating device accordingto claim 5 or 6, wherein a draft between said pair of measuring rollersand said pair of drawing-in rollers corresponds to a ratio of about1:1.05.
 9. A regulating device according to claim 5 or 6, wherein:a oneof said drawing-in rollers includes at least four generator marksstaggered to one another by approximately same angular intervals, towhich said fixed-frame sensor is allocated; and said measuring rollersare arranged to said drawing-in rollers, and said drawing-in rollers arearranged to said drafting rollers along a travelling direction of thesliver and staggered by about 50 mm each.
 10. A regulating deviceaccording to claim 5 or 9, further comprising:a can coiler includingmeans for sliver coiling following the drafting arrangement, said cancoiler being driven by a motor which is indirectly powered and dependentupon a speed of said variable speed motor.